(a) Field of the Invention
This invention relates to news inks and the like and, more particularly to news inks with controlled rheological characteristics. These inks are thus better suited to printing needs, especially in high speed presses, as they contain no potentially toxic hydrocarbons, and also give rise to a far lower degree of misting in use, without becoming too short.
(b) Description of the Prior Art
News inks are prepared generally by mechanically dispersing a pigment into a mineral ink oil. For many years the only pigment used in quantity was carbon black, but with the advent of colour print in newspapers, other colours are now used in larger quantities. However, black ink, based generally on some form of carbon black, still represents by far the largest proportion of the ink used. The oil used in preparing these inks serves as the single vehicle for the ink. Surprisingly, little detailed attention appears to have been paid, in the past, to mineral oil systems useful for ink oils, even though this usage represents a tonnage-scale level of consumption. For example, U.S. Pat. No. 3,615,754 (issued Oct. 26, 1971 to W. W. Gotshall) whilst being concerned with non-bleeding ink compositions, laconically remarks that "Any liquid varnish that is commonly used with ink formulations may be used here, such as . . . mineral oils . . . ". Similarly U.S. Pat. No. 3,199,991 (issued Aug. 10, 1965 to The California Ink Company) is reticent concerning ink oils.
In general, existing inks based on hydrocarbon oils suffer from at least one of a number of shortcomings. These are:
(a) misting; PA0 (b) poor colour brightness; PA0 (c) poor transfer quality; and PA0 (d) toxicity. PA0 Colour: water-white PA0 Aromatic content: zero PA0 Refractive index: 1.467-1.480 PA0 Specific gravity: 0.850-0.879 PA0 Viscosity, cSt/40.degree. C.: 9.38-439.7 PA0 Aniline point, .degree.C.: 96-138 PA0 Colour: water-white PA0 Aromatic Content: zero PA0 Refractive index: 1.4800 PA0 Specific gravity: 0.878 PA0 Viscosity, cSt/40.degree. C.: 317.8 PA0 Aniline point, .degree.C.: 134 PA0 Colour: water-white PA0 Aromatic content: zero PA0 Refractive index: 1.467-1.480 PA0 Specific gravity: 0.850-0.879 PA0 Viscosity, cSt/40.degree. C.: 9.38-439.7 PA0 Aniline point, .degree.C.: 96-138
As these four are relatively important to this invention, some comment upon each is desirable.
Misting occurs when the ink applied to a roller for printing purposes fails to stay on that roller while it is rotating. In modern printing presses using paper speeds of 1,000 ft/min to 2,000 ft/min, these inked rollers rotate with a high surface speed: in its turn, this places a high centrifugal force on the ink. Due to this force a proportion of the ink literally flies off, causing formation of an ink mist. Apart from being a waste of ink, and cause of cleaning problems, this mist also presents a significant environmental and health problem.
Poor colour brightness arises when oils which may have been found acceptable for black inks are used for colours, especially light colours such as pinks and yellows. The problem is that many ink oils are far from water-white; ink oil specifications often contain a colour limitation, for example the figure of 2.5, according to ASTM D-1500, to be found in the claims of U.S. Pat. No. 3,847,623 (issued Nov. 12, 1974 to Sun Oil Co.).
Poor transfer quality, which is associated with poor strike through, poor set off, and shortness, is connected, at least in part, with oil viscosity. Too high a viscosity causes shortness and lack of strike-through, where as too low viscosity will cause the reverse. It can also be seen from this that at least shortness and misting are, to a degree, interrelated, for lengthening an oil, for example by adding a solvent, will decrease its viscosity and hence tend to increase its propensities for misting.
Toxicity arises in two ways. Where misting is going on, it is harmful to the operator's lungs to be exposed to such an atmosphere containing minute oil drops. The second possibility is that these oil drops may contain within them substances injurious to health. While the use of lead and selenium-based pigments for colours has effectively ceased, many printing ink oils still contain proportions of aromatic hydrocarbons which either are proven to be potentially carcinogenic, such as benzene, or are believed to be potentially carcinogenic, such as toluene and polycyclic compounds. Clearly elimination of these from an ink is desirable for health reasons. Such an elimination would also have an indirect benefit. The printing presses commonly in use generally use rollers which have rubber surfaces, which are prone to swelling and softening by aromatic hydrocarbons. Elimination of aromatic-hydrocarbons from the oil will thus improve press roller life.